1. Field of the Invention
This invention relates to an open/close mechanism of an upper frame for use in an image forming apparatus such as a copying machine, a facsimile machine, a printer, and a compound machine having combined functions of these machines. The image forming apparatus comprises a main base frame, the upper frame rotatably linked to an upper end of the main base frame to open and close relative to the main base frame by a rotation of the upper frame about a pivotal axis of the upper end, and a brake force apply mechanism for applying a brake force to the upper frame.
2. Description of the Background Art
There has been known an image forming apparatus of a so-called shell type in which an upper frame is openably connected to a main base frame. In such shell type image forming apparatus, an operating unit provided with ten key switches and a start button, and an upper cover are arranged on the upper frame to constitute an upper unit, while the main base frame is internally provided with various elements such as an imaging unit and a recording paper transport unit.
An operator can easily access the inside of the image forming apparatus (i.e., inside of the main base frame) by opening the upper unit (upper frame) relative to the main base frame to remove recording paper jammed inside the apparatus or to replenish toner. Upon completion of the certain operation such as removal of jammed paper and toner replenishment, the operator closes the upper unit to restore the image forming apparatus in an initial state ready for image recording/reading operations.
Since the above image forming apparatus is constructed such that the upper unit closes the main base frame by its own weight, a well-known brake force supplier such as a gear damper and a torque limiter is provided in the apparatus to give a certain brake force to the upper unit that is being closed. The brake force supplier is adapted to reduce the closing speed of the upper unit.
The image forming apparatus provided with the above brake force supplier has suffered from the following problem. Since the brake force given to the upper unit (upper frame) is set to a constant value, it was difficult to control the closing speed of the upper unit stage by stage during a whole period from start of the closing operation to completion of the closing operation.
Observing the closing speed of the upper unit, the closing speed is relatively slow immediately after start of the closing operation. However, as the closing operation proceeds, the closing speed is accelerated. That is, the closing speed is not constant throughout the closing process.
If the brake force to be applied to the upper frame is set at a relatively low level, it is impossible to suppress the closing speed at a sufficiently low level immediately before the upper unit completely closes the main base frame (i.e., at the final stage of the closing operation) to avoid an impact force exerted on the main base frame.
On the contrary, if the brake force is set at a relatively high level, the closing operation of the upper unit at the initial stage becomes rather difficult unless an operator exerts a moderately large force at the start of closing operation.